1. Field of the Invention
This application is related to communications systems and more particularly to receivers of multicarrier systems.
2. Description of the Related Art
A typical superheterodyne receiver first converts a received radio-frequency (RF) signal to an intermediate frequency and then demodulates the intermediate-frequency (IF) signal using synchronous detection driven by a local oscillator having a frequency that is substantially the same as the frequency of the carrier signal for the intended data signal. A typical zero-IF (i.e., homodyne, synchrodyne, or direct-conversion) receiver is a receiver in which the local oscillator frequency is the same as the frequency of the carrier signal, so that mixing results in conversion directly to baseband (i.e., zero frequency). That is, a zero-IF receiver converts a received RF signal to a baseband signal using a single frequency conversion. A typical zero-IF receiver is less complex than a superheterodyne receiver since it requires fewer frequency conversions than a superheterodyne receiver, eliminates intermediate frequency stages, and reduces image rejection issues. The reduced complexity of a zero-IF receiver results in compact digital signal processing code size, efficient digital signal processing data manipulation, and reduced integrated circuit area.
However, a typical zero-IF receiver introduces a DC offset into the received signal. For example, local-oscillator energy can leak through the mixer stage, feed back to the receiver antenna input, and then re-enter the mixer stage. As a result, the overall local oscillator energy self-mixes and creates a receiver DC offset signal. The receiver DC offset could be large enough to overload any baseband amplifiers and degrade the recovery of an intended data signal. Typical receiver modifications that reduce the receiver DC offset include high-pass filtering the received signal, which increases the complexity of the receiver. The increased complexity is associated with higher production costs that may outweigh the benefits. Accordingly, improved techniques for recovering an intended data signal from an RF signal in a zero-IF receiver are desired.